1. Field of the Invention
This invention relates to fabrication and use of carbon nanotube Bucky paper “cages” for immune shielding of cells and tissues, for transplantation and other activities.
2. Description of the Related Art
Transplantation of cells and tissues from one human to another is limited by the host immune system, which identifies and rejects non-host cells and tissues with high efficiency. One strategy for avoiding or surmounting this barrier is to enclose the cells in a “cage” that provides a biological shield (an “immune shield”) that, it is hoped, will prevent the transplanted cells and tissues from being rejected by the host immune system. This strategy would have application in endocrinology (e.g., islet cell transplantation), gene therapy (transplantation of cells to provide a missing protein or to replace a dysfunctional protein), immune therapy, or other biological therapy (transplantation of cells to provide specific immunoglobulins, cytokines, immune regulators or biological response modifiers). Such a system could also provide a micro-environment, within a human or other host body, for tissue engineering, to allow for differentiation of cells or assembly of tissue structures with two-dimensional or three-dimensional architecture or the formation of nascent organs, for subsequent use in the host or elsewhere.
Immune shielding may also serve as an important strategy for preventing immune rejection of implantable medical devices that range in size from ultra-small scale nanoparticles and nanoprobes to large scale macroscopic devices. The strategy of immune shielding allows use of a wider range of materials in the construction of implantable medical devices than would otherwise be possible because of the presence of the host immune system.
Many materials have been proposed as immune shields, including specially treated biological and non-biological materials, silicon, ceramics, synthetic polymers and other non-organic materials. As a rule, these foreign materials tend to provoke an immune response in the host body, and this has limited development in this field. Another phenomenon associated with transplantation of foreign materials into a host is localized scar formation and/or obstruction of pores in the foreign material. The presence of pores is required in most biological applications for efficient transfer of nutrients and other biological factors into the interior of the cage, and efficient transfer of waste products, metabolites and secreted substances from inside the cage to outside the cage.
What is needed is a biocompatible material that can be formed into a “cage” or similar structure for containing cells or tissue that prevents or limits access by the host immune system to the foreign cells or tissue. The cage material should allow the cells and/or tissue to be maintained in a live and functioning state; and in some cases, should permit the cells and/or tissue to carry out normal (physiological) and specially engineered sensing functions and/or normal (physiological) or specially engineered secretory functions. The cage material itself should not provoke (or should limit significantly) an immune response in the host system. The cage material itself should not elicit (or should limit significantly) scar formation in the host that, together with an immune response, could lead to obstruction of the pores of the cage material. The cage material itself should resist protein deposition that, together with scar formation or an immune response, could lead to obstruction of the pores. Preferably, the material should be flexible and sufficiently resilient to withstand the forces that may be involved in surgical implantation or transplantation and other forces that may be present in the host environment. The material should be configurable into a variety of geometric shapes, to optimize transport of substances across the cage and to promote the maintenance of cells and/or tissues.